A low anion gap stems from an imbalance in the body’s pH levels. Healthcare professionals identify this “gap” by looking at the results of a blood test that measures electrolyte levels.
To maintain health and function, the body needs a pH balance. This refers to balanced levels of acids and alkali, or bases, in the blood.
If a person has a pH imbalance, they may have high acid levels, called “acidosis,” or high levels of bases, known as “alkalosis.”
Electrolytes are substances that have an electrical charge. This helps them maintain the body’s pH balance. They are vital for many bodily functions. Examples of electrolytes include sodium, potassium, chloride, bicarbonate, and other minerals.
Below, we explore the causes, symptoms, and treatments for a low — or a high — anion gap reading.
Normal anion gap readings range from 3–10 milliequivalents per liter. Readings outside this range may indicate a pH imbalance, and this can stem from a wide variety of health issues.
Having an anion gap reading in the low range is very rare, and it may stem from a laboratory error. If an electrolyte blood test shows a low anion gap, a doctor usually orders a second test.
A condition called hypoalbuminemia can cause a low anion gap reading, but this is less common than a laboratory error.
This involves having too little of an essential protein called albumin in the blood. Hypoalbuminemia usually occurs because of inflammation throughout the body.
Specific causes of hypoalbuminemia include:
- recent surgery
- severe burns
- liver or kidney disease
- hyperkalemia, which is high potassium
- hypercalcemia, which is high calcium
- hypermagnesemia, which is high magnesium
- lithium toxicity
Hypoalbuminemia and a resulting low anion gap
When a person has too much acid or too little alkali in their blood, the anion gap reading will be higher than normal. This is called “high anion gap metabolic acidosis,” and it can be life threatening in some situations.
This type of acidosis may result from:
- uncontrolled diabetes
- kidney damage or failure
- certain medications, including metformin
- lactic acidosis, which is a buildup of lactic acid
- excessive alcohol use that causes alcoholic ketoacidosis
- exposure to high levels of aspirin, methanol, or antifreeze, among other chemical substances
- a drug overdose
- prolonged starvation
The symptoms of a pH imbalance depend on the cause.
Health-related factors associated with a low anion gap are unlikely to cause symptoms. And in most cases, this reading stems from a mistaken calculation.
A person with acidosis, and thus a high anion gap reading, may have no symptoms or have symptoms related to the underlying health issue. These symptoms may include:
- nausea, with or without vomiting
- a headache
- shortness of breath
- a rapid heart rate
- low blood pressure
When a person has higher levels of alkali in their blood, they may also have:
- low calcium levels
- a headache
- seizures, muscle spasms, and delirium
- heart palpitations
Treatments can address the health issue responsible for an abnormal anion gap reading.
Measuring the anion gap alone cannot confirm any diagnosis, so a doctor performs a variety of other tests before making a diagnosis and a treatment plan.
Anyone concerned about a high or low anion gap reading should discuss the possible cause with their doctor.
A range of medical conditions can disrupt the balance of the body’s pH levels. Calculating the anion gap can help a doctor determine the cause of an imbalance.
A low anion gap reading is very rare, and it often results from a laboratory error. As a result, a doctor who finds a low reading typically orders a second test.
A high anion gap reading often signals a serious health problem, such as uncontrolled diabetes or a drug overdose. The person usually needs prompt treatment to prevent severe or fatal complications.
A doctor can provide more specific information about the likely cause of a low or high anion gap reading.